1. Technical Field of the Invention
The present invention relates generally to a magnet switch which may be employed in an engine starter working to start an internal combustion engine of automotive vehicles, and more particularly to an improved structure of such a magnet switch designed to have improved resistance to impact shock occurring during operation of the magnet switch without increasing production costs.
2. Background Art
Japanese translation No. 2002-524826 of a PCT internal patent application teaches a magnet switch which is, as illustrated in FIG. 20, equipped with a disc assembly made 110 of a stack of annular sheets 111 and a cylindrical core body 100 disposed in alignment with a plunger (i.e., a movable core). The cylindrical core body 100 is fit in a center hole 112 of the disc assembly 110. Terminal leads of a magnetic coil extend in an axial direction of the magnet switch through grooves formed in the periphery of the disc assembly 110. The outermost one of the annular sheets of the disc assembly 110 has a tab 400 formed by cutting and bending a portion thereof for retaining the terminal leads of the coil.
The above structure, however, has the following drawbacks. The installation of the disc assembly 110 on the cylindrical core body 100 requires the alignment of recesses formed in the periphery of the annular sheets 111 which define the grooves through which terminal leads of the coil extend. Specifically, it is necessary to align the recesses in sequence so as to coincide with one another upon the installation of the disc assembly 110 on the core body 100. Alternatively, it is necessary to align the recesses of the annular sheets 111 to make a stack thereof and then fit the stack on the core body 100. This is, however, very troublesome and requires upskilling workers.
Additionally, the tab 400 formed on the outermost one of the sheets of the disc assembly 110 obstructs soldering of the end of the coil to the disc assembly 110, thus resulting in a decrease in workability.
Further, when the coil is excited, and the plunger hits the core body 100, it will cause the impact to be transmitted to the end of the coil soldered to the surface of the sheets of the disc assembly. The disc assembly is, therefore, designed to form the tab 400 for withstanding the impact. This results in an increase in total production const of the magnet switch.
The core body 100 is, as can be seen in the drawing, made up of a base 101 and a boss 102. The base 101 faces the plunger. The boss 102 extends from the base 101 away from the plunger.
When the magnet switch is open or closed so many times, it may cause the boss 102 to escape from the center hole 112. Specifically, when the sheets 111 of the disc assembly 110 are each punched out to form circular holes defining the center hole 112, it may result in a variation in inner diameter among the sheets 111, deformation in shape of the circular holes, or a lack in sheared area of the circular holes, which leads to a lack in degree of press-fitting of the boss 102 to the center hole 112 of the disc assembly 110. Therefore, when the plunger is being attracted to the base 101, the reactive force or compressive pressure, as produced by a drive spring installed in the plunger, may pull the plunger to dislodge the boss 102 from the disc assembly 110.